1. Field of the Invention
The present invention relates to a low intermediate frequency (IF) receiver, and more particularly, to a low IF receiver of rejecting an image signal to minimize image components in a radio frequency (RF) signal.
2. Description of the Related Art
FIG. 1 is a block diagram illustrating a conventional low intermediate frequency (IF) receiver.
Referring to FIG. 1, the conventional low IF receiver 100 includes an antenna, a low noise amplifier (LNA) 110, a quadrature I/Q mixer 120, a signal complex filter 130, and a variable gain amplifier 140.
The antenna receives electromagnetic waves Sin in the air. The LNA 110 amplifies a radio frequency (RF) signal while rejecting noise in the received signal Sin as much as possible. The quadrature I/Q mixer 120 down-converts the RF signal into an IF signal in a baseband which is a frequency band including original signals by removing a carrier frequency to generate an I signal and a Q signal. Since the down-converted signals include signals in various channels, the signal complex filter 130 which performs a band pass filtering function selects signals in a desired channel from the down-converted signals. Since the received signal Sin cannot be sufficiently amplified by using only the LNA 110, and a signal amplification ratio has to be accurately adjusted, the variable gain amplifier 140 amplifies and outputs the signal received from the signal complex filter 130.
The low IF receiver 100 performs a function of receiving the RF signal. The RF signal includes an image signal in addition to a real signal that is to be received. Here, the image signal is not a signal internally generated when the mixer 120 of the receiver 100 performs mixing but an externally received signal such as a signal in an adjacent channel. When the mixer 120 down-converts the RF signal Sin into the IF signal, both the real signal and the image signal are down-converted on the basis of the IF frequency.
As described above, the image signal that is simultaneously down-converted works as a quantity of interrupting demodulation of the received signal. Therefore, how much quantity of the image signal is rejected determines selectivity of the low IF receiver.
Conventionally, in order to improve the performance to reject the image signal, a digital signal processing method is used. In this method, a high-performance analog-to-digital (ADC) converter converts an analog signal into digital signal, and a digital filter rejects an image signal in the digital signal and selects only a desired signal.
According to the aforementioned method, there are problems in that a construction of a receiver system is complex, and manufacturing costs are increased.